How much saline should be added to the tube in which the vaginal swab is placed for transport to the lab?
The correct answer and explanation is:
Correct Answer: Typically, 1 to 3 milliliters (mL) of sterile normal saline (0.9% NaCl) should be added to the tube for transporting a vaginal swab to the laboratory.
Explanation (300 words):
When collecting a vaginal swab for laboratory analysis—whether for microbiological culture, wet mount microscopy, or nucleic acid testing—the sample must be transported in a way that preserves the integrity of the specimen. One widely used method is suspending the swab in sterile normal saline solution.
Why saline?
Normal saline (0.9% sodium chloride) is isotonic and mimics the osmotic conditions of the human body. This ensures that the cells and microbes present on the swab are not lysed or damaged during transport. It’s especially important for tests like wet mounts, where motility (e.g., of Trichomonas vaginalis) needs to be preserved for microscopic examination.
How much saline is used?
The standard practice is to place the vaginal swab in a sterile tube or vial containing 1 to 3 mL of saline. This volume is sufficient to:
- Submerge the swab completely
- Release and suspend the cellular material and organisms
- Provide enough sample volume for multiple lab tests if necessary
Best practices:
- Use sterile technique to avoid contamination.
- Label the sample properly with the patient’s information and time of collection.
- Transport the specimen to the laboratory immediately, or refrigerate it if there is a delay (depending on the test requirements).
Some laboratories may provide pre-filled saline transport tubes, especially when conducting specific tests like vaginal pH testing, wet mount microscopy, or Gram stain.
Note: If the swab is being used for other tests like PCR or STI panels, a different medium (such as a molecular transport medium or Amies medium) may be required, so always follow lab-specific protocols.